Category Archives: Exoplanets

For three days in early October, the South Cloisters and Garden Room of UCL played host to a festival of astronomy – Your Universe. Organised by Francisco Diego and Farah Islam from the department of Physics and Astronomy, the event was divided into two school days and one Saturday for the general public. The events saw demonstrations and explanations of different aspects of astronomy delivered by researchers in the department as well as two lectures, one each on Friday and Saturday evening.
The quiet and darkness of the Garden Room saw three presentations. The first was a powerpoint presentation on exoplanets – planets orbiting stars other than our Sun – delivered by David Johnson. The second was the Magic Planet, a globe onto whose inner surface was projected the atmosphere or outer surface of the Sun, several planets and satellites in turn. Finally, a demonstration of spectroscopy and the fingerprints of colours emitted and absorbed by individual elements was given by Gleb with lamps and spectroscopes capable of splitting light into the rainbow of available colours.
In the South Cloisters, another five demonstrations lay in wait. Firstly Emily Hall expanded minds with a talk on cosmology, discussing Dark Matter, that mysterious thing that interacts only gravitationally with normal matter, and Dark Energy; the curious driving force behind the expansion of the universe. Next came a demonstration of robotic telescopes controlled over the internet from a NASA and Harvard maintained website. The third talk took in the life cycle of stars and an explanation of the HR diagram that astronomers use to categorise stars. The fourth demonstration was telescopes, including scopes either looking at the Sun in the light of hydrogen atoms or, during less clement weather, at postcards at the other end of the South Cloisters, and a display on the University of London Observatory, used by UCL students studying astronomy. Finally, a demonstration of the timescales involved in the creation of life and the universe rounded off the main set of events.
Outside of the main event, more sedate displays in the Octagon and North cloisters were within easy reach of guests. These included an orrery, showing the motions of planets and major satellites around the Sun and a book of satellite images open at plates showing the Earth and Moon as seen by Lunar Orbiter 5. In the North Cloisters, the entire length of the space had been taken up by Pete Grindrod’s display; a high resolution image, ten miles of the surface of Mars as seen by the HiRISE camera on the MRO satellite, presently in orbit of the Red Planet.
With eight groups of primary and eight secondary age pupils per day, we saw around five hundred school children pass through the displays during the first two days and more than another hundred members of the public on Saturday. They also enjoyed two lectures; Mikako Matsuura’s description of seeing star birth through the eyes of the Herschel infrared space telescope and Francisco Diego’s answer to the question of why have we not found evidence of aliens.

There seems to have been two press conferences going on when the discovery of the planet Gliese 581g was announced…

The first press conference was the announcement of a scientific study of the motions of the star Gliese 581 (also known as Gliese 581a). These motions, studied over eleven years, have suggested the existence of a planet 3.1-4.3 times the mass of the Earth orbitting the red dwarf in around 37 days, putting it within the ‘habitable’ zone of the star in terms of equilibrium temperature derived from the radiative balance of the system. This press conference included some ruminations on what would be needed to find the signals of life, such as spectroscopy of the atmosphere, which due to the alignment of the system, cannot happen with present techniques. This aspect of that press conference and the implications for the search for life outside the solar system are discussed here.

The second press conference focuses on what seems to be either over-excitement by discoverer Steve Vogt or over excitement by those reporting his thoughts and words when discussing the inevitability of life on the planet Zarmina. It is entirely common for authors of a study to contemplate the implications it could have and the possibilities it opens, and obviously where life in the cold recesses of space are concerned, the possibilities are particularly enticing, but in order to prevent more canals of Mars, Venusian cities and other such hostages to fortune, it helps to avoid statements such as life being 100% certain. But if you do want to get lost in the imagery, Vogt expands on it here.

A quick roundup of articles on newly discovered habitable zone extrasolar rocky planet. Start off at the overoptimistic end with the Telegraph’s article, taking Vogt’s rather dodgy assumption that it is certain there’s life there at face value… Then there’s Skymania, which mentions the possibilities of life on the planet, while stressing these are just possibilities. Discovery puts in a line suggesting life is so certain, it would be harder to prove it isn’t there. Next to fall in line is the BBC article, mostly neutral but pushing the life angle hard. Then onto the more neutral press release from the University that hosts the researchers involved. Finally, Universe Today hosted a twitter debate on whether or not Vogt was right to be confident of life’s appearance on the planet. It did not tilt in his favour to say the least…

Gliese 581 is a name well known and repeated in exoplanetary circles. Lying 20.3 light years from us in the constellation of Libra, it is a red dwarf star now known to have at least six planets. Twice before, the star has been in the news with one of its planets declared close to the habitable zone – the slender band of orbits around the star where the stellar radiation is high enough to melt ice, but low enough not to boil water. Planet C was close, but on the hot side, too close to the star. Planet D was close, but on the cold side. Now a planet G has appeared and it is right in the middle of the habitable zone.

Appearing in this region around a star is not in any way proof that a planet can support life, it is merely a suggestion that it is likely to fulfill at least one of the prerequisites – the balance of radiation from its host star is sufficient to sustain liquid water. But further properties derived from observations of the star are quite positive. The planet is 3-4 times the mass of the Earth, suggesting a rocky planet with a defined surface, which at a similar density would put it at 1.2-1.4 Earth masses, giving a surface gravity not that dissimilar to our own. That would imply sufficient gravity to hold an atmosphere. But the similarities with the development of our own world do seem to end there.

The planet orbits its host star in 37 days. The low luminosity of Gliese 581 means that to be in the habitable zone in terms of radiation, the planet must crowd close to the star. This means the star has sufficient gravitational effect to tidally lock its satellite – meaning as with the Moon in orbit of the Earth, the same face of the planet always points toward the star. This would imply a searingly hot one face and freezing cold dark side, with winds racing from one side to the other. At the day night boundary, buffeted by these winds, more moderate climates would be seen at the different latitudes, where life could start, possibly evolving to take advantage of less temperate spaces on the planet after leaving the cradle. Red Dwarfs are long lived stars, so the time will also be there to do it.

But gravity and photons aren’t all a star can put out. Gliese 581 isn’t a flare star, that is, it isn’t known for sudden massive bursts of material from its surface, but it will still lose mass through slow stellar winds. It is believed that planets in close orbits to their host stars tend to lose their magnetic fields, or see them closely affiliated with that of their host stars. The protective magnetosphere, the magnetic sheath that protects us against the particle radiation that results from hot matter essentially expanding off the surface of our Sun, may not be replicated in this new place.

Whether or not there is life in this increasingly diverse place, the careful measurements carried out by the team, who measured the Doppler shifts of the light from the wobbling star to an amazing precision, do show that pulling out rocky planets in the habitable zones is within reach of modern technology. However, with the actual light from the planet lost in the glare of the star, it will take time and new technology to tease out the signal of life within that light, should it be there.

The paper announcing the discovery of the planet is here and one submitted at the same time detailing modelling of planet D’s atmosphere to determine whether or not its properties are sufficient to insulate the bitter cold and foster life is here.

Spotting exoplanets is very hard to do directly. The best bet is to find an indirect method, such as the amount of light they block from their host star, the gravitational lens they produce as they pass between us and another object, or the amount they pull their host star about. Another suggestion is to look for how they alter the distribution of debris in their version of the solar system. Round these parts, the outer debris ring is the Kuiper Edgeworth belt, and just like Saturn’s rings are shepherded by Saturn’s moons, so this belt is kept in line by the planet Neptune. Looking for well kept borders enables some idea that a planet may be available, but when looking at even earlier times in a solar system’s formation, the evidence of an outer planet’s influence can be even easier to spot.

NASA researchers have now modelled the effect of Neptune on the belt, going back to the earliest times in the solar system’s history. They find a well kept belt forms in around 15 million years. The researchers plan to extend their findings to researching the main asteroid belt as well as the capture of Trojan asteroids by gravitational sources associated with Jupiter. They will also investigate models of dusty rings seen in other planetary systems to see what information can be obtained. Further information and a video of the creation of our outer ring can be seen here.

By which I don’t just mean our Moon, but various moons through the solar system, some of which have been in the spotlight.

Starting out at both Saturn and Earth – and the two are united in having Moons that are slowly shrinking as they cool, the effect being, as on Earth and more dramatically on Mercury, that the outer layer develops wrinkles, seen as mountain chains. Cassini made the discovery for Titan when mapping the icy world’s topography. Ripples of mountains, all orientated the same and clustered around the equator fitted a computer model of a small body, made of ice and rock with a subsurface ocean, slowly cooling over time as radioactive isotopes decay away. This causes the body to shrink, but the outer parts of the subsurface ocean to freeze and expand. Losing seven kilometres in radius and one percent of volume over the four billion or so years since formation, Titan has achieved two kilometre high mountains in its equatorial ranges. The features seen on our own Moon, by comparison, are much shorter – nine metres or so – but run on for kilometres and cover the whole surface. Equatorial ‘lobate scarps’ were first seen by the Apollo program, but only at the equator. More recent observations with the Lunar Reconnaissance Orbiter have identified further scarps dotted around the Moon. estimates of the shrinking of the Moon from the features suggests around 100m has been lost in around 800 million years, putting the Moon at a lower rate of radius loss than Titan. There is also the suggestion that instabilities in the contraction process are responsible for some of the Moon-quakes observed with Apollo hardware.

Titan wasn’t the only moon under the microscope of Cassini. During one flyby, the probe took images of three moons – Enceladus, Tethys and Dione. Images like this enable scientists to look at changing shadows on the surface of different moons that may help to eke out a little extra detail, or may even reveal a new area of the surface in unprecedented resolution at a given wavelength. They also help others to create computer models of moon surfaces for virtual flyby videos like these.

Of course, they’re also good just for being nice pictures. Stuart Atkinson has put up a post with one of the Enceladus pictures taken by Cassini, and another picture taken from the Mercury bound Messenger probe of a planet and a Moon. The planet happens to be Earth. Messenger wasn’t idly glancing into the void, however, the image was taken during a sweep for Vulcanoids – asteroids lying between the Earth and the Sun, unseen by terrestrial observatories due to the glare of our nearest star. These particular asteroids, should they exist, would be trapped in orbits that never take them as far out as ourselves, rather than actual asteroids or spent comets that have drifted inward. They shouldn’t exist, according to prevailing ideas on the formation of the solar system, so if just one is seen and later confirmed, it would be interesting. It would also mean that alongside the Oort Cloud, the Kuiper-Edgeworth Belt and the Asteroid Belt, we’d also have a Vulcanoid Belt, with new objects to study and slot into the history of the solar system.

For now, we’ll just have to study the solar system through the most ancient rocks available to present day geologists. The most recent block of ancient rock to be found has been dated at around 4.45 billion years old. The Earth is estimated to be 4.54 billion years old and so should the result be confirmed, the arctic rocks would date to a period before the crust of the Earth had formed, but after the core was created. The scientists measured the age looking at well known radioactive decay signatures, though others have suggested a better way would be to look for signatures from istopes believed to be around at the time, but which quickly decayed away in the earliest parts of terrestrial history.

The past and future evolution of planetary systems can have an impact on whether or not there are moons to be found. Hot Jupiter planets – gas giants that have migrated closer to their parent stars – are unlikely to have held onto their moons as they rode the gravitational turbulence further in and dealt with the gravitational forces from the closer proximity to their host star according to new research. Exomoon hunters (like David Kipping, quoted in the article) aren’t detered as the planets do still provide a testbed for observational techniques until our methods and instruments become capable of tackling extra solar planets with a higher likelihood of companion bodies.

Finally, the troubled evolution of Jupiter has been in the news (along with the evolution of its clouds, visible even in relatively small telescopes). The largest of our solar system’s planets has a small problem – its core is a little depleted compared to that of second largest planet Saturn. Current theory suggests that gas giants start out as a giant rocky/ice body, perhaps ten times the mass of the Earth, which then gravitationally hoovers up the gas surrounding it. The trouble is while Saturn shows evidence for the right size of core, Jupiter is a little lacking given its incredible overall mass. A new suggestion has been made that Jupiter’s own core has been in collision with four or five super-Earth’s, each skimming a bit off the top. It is hoped that the forthcoming Juno mission will be able to add observational evidence to the idea.

The summer brings a little relief to undergraduate students in universities as they head off for a break, but it also provides some variety to researchers as they cram as many large meetings in foreign climes as possible into this area of the year.

Jonathan Butterworth has been writing a blog or two for the Guardian regarding the ICHEP2010 meeting for high energy particle physicists and particle astrophysicists of all flavours. Apart from me. The meeting has already generated several related stories including this one pointing out energy ranges where they’re pretty sure the Higg’s boson (particle responsible for mass) no longer can be thought to exist and the remaining likely energies left to explore. Since 2001, Fermilab has explored and ruled out one quarter of those energies. The tentative schedule for the next decade of the Large Hadron Collider was also published at the meeting, with the next three years set to be a tussle between it and the Tevatron for exploring that final area of energy as well as performing all the other experiments required of such machines.

One conference going on now is Molecules in Galaxies, which is being live-tweeted by Chris Lintott (he of the Sky at Night and the Zooniverse). Interesting things featured include the Cosmic Eyelash, a gravitationally lensed galaxy full of starbirth lying in a distant recess of the universe, magnified by an intervening galaxy cluster.

Not all conferences of interest are officially academic, however. In the recent TEDGlobal conference, whose talks are put online, Dimitar Sasselov, a Kepler scientist has released to the world the size distributions of the four hundred exoplanets the team behind the space telescope are keeping under wraps for further analysis, added to those confirmed previously. They show a strong tendency in the data toward Earth sized planets, with an enormous 130 candidate planets coming out at around twice our size or less (down to around one Earth radius, which is around the limit of Kepler’s sensitivity). Now size doesn’t mean like, and indeed if they do have an Earth-like candidate in the list, it won’t be confirmed for some time as it would have to be orbiting another year before it is seen to dim the light of its star again and Kepler just hasn’t been staring that long. It should be said, the first paper I saw this in wasn’t a refereed journal paper, but the Sunday Times. The size distribution was announced a while ago (so why the hysterics from NASA Watch?), but this is the first nicely packaged graph of what it would look like, should the recent 706 candidate planets be confirmed. What the distribution could mean, more importantly, is that Earth sized worlds dominate the scene, so although we appear to be spotting big planets all over the shop now, smaller dots are even more prevalent. As I mentioned earlier, Kepler’s limit is around Earth sized, so imagine now going down to Venus size, or Mars size – how many of those worlds could be out there? Under the radar? If they’re in an Earth-like orbit around a Sun-like star, even a Kepler mission with suitable sensitivity would be unable to tell officially until three orbits had been registered.

And now onto two upcoming meetings. September will see Desert RATS, NASA’s annual display of new space technology crawling over terrain matched to another planet. We know the what and the when, but what about the where? Well, this time it is up for a vote. NASA can’t decide and wants your opinion through this website.